The present invention relates to a method of manufacturing an impeller rotor assembly. More specifically, the invention relates to a technology used in the manufacture of a rotor assembly integrated with an impeller, whose aim is to prevent cracks on the inner and outer surfaces of a rotor magnet that may occur due to sudden temperature changes during mold forming through the injection of hot molten resin by providing small space between the rotor magnet and the yoke designed to support said magnet.
Conventional impeller rotor assemblies generally used in automotive water pumps are built as an integrated structure comprising a cylindrical magnet with hollow space through which it can be integrated with a rotary shaft, and a magnet yoke and an impeller that are formed in a plastic resin mold.
In this process by which magnets and magnet yokes are produced as integrated structures, when plastic resin is injected to form a mold under high temperature, the outer surface of the magnet cools too quickly and shrinks whereas the inner surface cools relatively slowly, and such cooling speed differences between outer and inner surfaces have resulted in cracks. Furthermore, since the magnet yoke attached to the inner surface of the magnet increases the temperature gradient difference between inner and outer surfaces of the magnet, causing cracks on the magnet surface.
The conventional technology related to the above-described problem is the hot water boiler featuring an impeller assembly with enhanced assembly workability patented under Republic of Korea Patent Registration No. 10-0943726.
In this conventional method intended to enhance workability in the assembly of the impeller and the magnet using a guide apparatus, cracks on the inner circumferential surface of the magnet can be reduced with no mold-forming process. However, the technology involves problems with durability and, due to the way in which its parts are combined, it is not suitable for the impellers used in pumps that require high rotational speeds.